Proposal

In towns villages and cities, we use "highway=unclassified" to mark pretty much all residential roads. Unclassified refers to any normal public road, but is usually a 2-lane road which can accept reasonable amounts of traffic-flow.

They're still 2-way public roads, and you can drive down them in a car if you're careful. But there's only room for one car width maximum, and if you meet someone coming opposite direction, will have to reverse.

The tag highway=service gives an ideal rendering for these roads, since it shows like an unclassified road, but with visibly narrower width that can be seen on town plans.

Since a narrow lane isn't technically a wikipedia:Service road though, it would be useful to have a proper tag for these things.